A starry night at Paranal, one of the world's finest observing sites. The observatory's four massive 8.2 meter telescope units are situated on top of the 2,600 meter high mountain, Cerro Paranal, in the dry Atacama Desert in northern Chile. The individual unit telescopes can be used separately or in combination. The yellow light from one of the domes is a laser guide star for Adaptive Optics (AO), a technology to improve the performance of optical systems by reducing the effects of rapidly changing optical distortion, most commonly used to remove the effects of atmospheric distortion. AO systems require a wavefront reference source in order to correct atmospheric distortion and because bright stars are not available in all parts of the sky, the system shine a laser into the atmosphere to create a yellow artificial "star" in the 95 km altitude sodium cloud around the Earth. Serge Brunier/Sergebrunier.com.